1. Field of the Invention
The present invention relates to elastic wave apparatuses, and, more particularly, to an elastic wave apparatus including a base substrate and an elastic wave filter provided with cascaded resonators.
2. Description of the Related Art
In order to cause an elastic wave apparatus including an elastic wave element using an elastic wave such as a surface acoustic wave or a boundary wave to efficiently perform heat dissipation, a method of disposing a heat-dissipation dummy electrode has been proposed.
For example, as illustrated in a block diagram in FIG. 13, each of surface acoustic wave filters F1 and F2 includes resonators 117. An input electrode 118, an output electrode 119, and ground electrodes 120, which are electrodes related to the electrical operations of the resonators 117, are connected to the resonators 117 via wiring lines 121. Heat-dissipation electrodes 122 that are not related to the electrical operations of the resonators 117, that is, dummy electrodes, are formed. The resonator 117 includes a comb-shaped IDT electrode 117a and reflectors 117b. Some of the heat-dissipation electrodes 122 are directly connected to the reflectors 117b, some of them are electrically connected to the reflectors 117b via the wiring lines 121, and some of them are provided independently of the resonators 117 and the electrodes 118, 119, and 120.
As illustrated in a cross-sectional view in FIG. 14, a blanching filter 110 including the surface acoustic wave filters F1 and F2 is provided with a mount board 111. The mount board 111 includes an element mount layer 111a on which the two surface acoustic wave filter F1 and F2 are mounted, a ground layer 111b at which a ground electrode is formed, a circuit forming layer 111c at which a high-frequency circuit such as a phase matching circuit is formed, and a substrate connection layer 111d at which a common ground electrode and external connection terminals 112 are formed, and is made of ceramics or a resin. The surface acoustic wave filters F1 and F2 are hermetically sealed with a cap 113, thereby being packaged. The layers included in the mount board 111 are electrically connected via through-hole conductors, via-hole conductors, or wiring lines 115 including side wall wiring lines formed on side surfaces. On the surfaces of the layers, the wiring lines 115, such as microstrip lines, are formed.
The mount board 111 and the input electrode 118, output electrode 119, ground electrodes 120, and heat-dissipation electrodes 122 of the resonators 117 are connected via projecting electrodes 114 illustrated in FIG. 14. The heat-dissipation electrodes 122 are electrically connected to a wiring line other than an input wiring line and an output wiring line formed at the mount board 111, that is, a wiring line connected to the ground electrode of the mount board 111 or a wiring line that is merely routed and has an unstable potential (see, for example, Japanese Unexamined Patent Application Publication No. 2003-101374).
Since the heat-dissipation electrodes 122, which are different from the input electrode 118, the output electrode 119, and the ground electrodes 120, are disposed at electrically unrelated positions in each of the surface acoustic wave filters F1 and F2, it is difficult to miniaturize the elastic wave apparatus illustrated in FIGS. 13 and 14.
Since no electrode that produces a heat-dissipation effect is not connected to the interstage portion (a portion cascading the resonators 117) that is very prone to reach high temperatures and the number of heat-dissipation paths is small, heat dissipation is not properly performed.